Over a recent number of years, there has been a strong movement within the surgical community toward minimally invasive therapies. The main goals of the minimally invasive therapies include: 1) eradication of targeted tissue, 2) decreased hospitalization time, 3) limited postoperative morbidities, 4) shortened return interval to daily functions and work, and 5) reduced overall treatment cost. One minimally invasive method of treating a disease state is through tissue freezing, also known as cryotherapy. Currently, cryotherapy is used to treat numerous disease states including organ confined tumors such as prostate, kidney, liver, as well as cardiovascular disease, retinal detachment, pain management, and other illness/disease states.
Cryotherapy is an effective yet minimally invasive alternative to radical surgery and radiation therapy. The procedure is done under either general or epidural anesthesia. The procedure offers patients a quicker recovery and reduced severity of potential side effects. Without the expense associated with major surgery or an extended hospital stay, cryotherapy is also a cost-effective treatment option.
The approaches utilized to date have focused on the delivery of liquid cryogen through the use of moderate to high pressure on the entire system or piston and bellows compression to drive fluid movement. At present, current systems utilizing liquid nitrogen operate at pressures between 14-480 psi; the systems in use cannot operate or withstand pressures greater that about 500 psi. Further, the use of heat exchangers have been limited to coils placed into a bath of cryogen to allow for time consuming, inefficient passive subcooling of the cryogen in which activation of these devices circulate a cryogen (such as liquid nitrogen) to a probe to create a heat sink, thus resulting in tissue freezing.
There exists a need for improvements in cryotherapy, and medical devices or components associated with the treatment, to better circulate liquid cryogen to a cryoprobe, to provide for rapid delivery through small tubes, and to facilitate improved measures for treatment and cost. The system of the present invention will allow for the circulation (cooling, delivery, and return) of liquid cryogen to a cryoprobe for the freezing of target tissue. The invention will facilitate the eradication of tissue, decrease hospitalization time, limit postoperative morbidities, shorten return to daily functions and work, and further reduce the overall treatment cost. Desirably, these improvements to device design and application will also increase its utilization for the treatment of multiple disease states.
One such category of diseases includes cardiac arrhythmias, a significant health problem. Atrial fibrillation is a common cardiac arrhythmia. Although atrial arrhythmias may not be as fatal as frequently as ventricular arrhythmias, atrial arrhythmias increase risk factors for other conditions such as embolisms. Further, atrial arrhythmias can contribute to the onset of ventricular arrhythmia.
Specifically, atrial fibrillation is a condition that results from the abnormal electrical activity within the heart. This abnormal activity may occur at regions of the heart including the sinoatrial (SA) node, the atrioventricular (AV) node, or within other areas of cardiac tissue. Moreover, atrial fibrillation may be caused by abnormal activity within one or more focal centers within the heart, the electrical activity generally decreasing the efficiency with which the heart pumps blood. It is believed that these foci can originate from within the pulmonary veins of the atrium, particularly the superior pulmonary veins. Therefore, it is also believed that atrial fibrillation can be controlled by structurally altering or ablating the tissue at or near the focal centers of the abnormal electrical activity to form a “conduction block”.
In one method, during open-heart surgery, and known as a surgical or epicardial ablation, the tissue of the heart and pulmonary veins is altered by making a series of incisions in a maze-like pattern in the atria and sewn back together (may be referred to as the “Cox maze” procedure). As the incisions heal, scar tissue forms, and the scar tissue may block the conductive pathways thought to cause atrial fibrillation.
Probe devices in the prior art have been designed for use directly in an open chest mode for the creation of linear cryogenic or radiofrequency (RF) lesions applied directly to an exposed heart. Parallel probe members have been used to create lesions through the tissue thickness, one member penetrating the myocardial tissue to the inside of an atrial chamber and cooperate with a member on the outer surface. Other designs have penetrated into the pericardial space using a subxiphoid or thoracic transcutaneous approach. Such probes may be used in conjunction with an endocardial catheter or other stimulation device to treat ventricular tachycardia (VT).
On the otherhand, a less invasive method of structurally altering tissue of the heart and pulmonary veins involves ablating tissue through the use of an ablation catheter, also known as endocardial ablation. The techniques typically are characterized by the application of energy to create lesions at the foci or other areas possessing abnormal electrical activity. Ablation catheters can also be used to create lesions at the heart to block electrical signals or alter a travel path of electrical signals at the heart. One example of an ablation catheter delivers RF energy to ablate tissue. Another example of an ablation catheter delivers cryotherapy to ablate tissue by freezing it.
Cryotherapy may be delivered to an appropriate treatment site inside a patient's heart or circulatory system with a cryotherapy catheter. This method, termed cryoplasty or cryotherapy may be used to cool or otherwise freeze a portion of target tissue to ablate the target tissue. A cryotherapy catheter generally includes a treatment member at its distal end, such as an inflatable balloon having a cooling chamber inside. To deliver the cryotherapy, the inflatable balloon may be introduced at a treatment site inside a patient, and the balloon positioned and then inflated. Once in position, a cryogenic fluid may be provided by a source external to the patient at the proximal end of the cryotherapy catheter, and delivered distally through a lumen to the cooling chamber, where it may be released. Release of the cryogenic fluid into the chamber can cool the chamber (e.g. through the Joule-Thompson effect), and correspondingly, with the balloon's outer surface, which may be in contact with tissue that is to be ablated. Gas resulting from release of the cryogenic fluid may be exhausted proximally through an exhaust lumen to a reservoir or pump external to the patient. As a result of the release of the cryogenic fluid into the chamber and the exhausting of the resulting gas from the chamber, tissue adjacent to the balloon may be cooled to a therapeutic level (e.g. 0° C., −20° C., −60° C., −80° C., or some other appropriate value) for an appropriate period of time.
For example, cryoplasty may be used to cool or freeze, and simultaneously dilate a lesion within a blood vessel that might otherwise lead to restenosis or recoil. Cryotherapy may also be used to create lesions in a heart to treat atrial fibrillation. However, creating lesions in a heart using cryotherapy poses a challenge in the delivering sufficient cooling to create a transmural (i.e., a through thickness) lesion. In addition, blood delivered to and from the heart constantly provides heat to a target site at the heart, thereby counteracting the cooling being delivered by the cryotherapy and limiting the amount of cooling that can be delivered to the target site. This in turn, further prevents a transmural lesion, or lesion of a desired size or characteristic, from being created at the target tissue. Thus, there is currently a need for an improved device and method to perform ablation therapy. The device would address an important aspect of treatment by providing lesions, transmural and continuous in character (otherwise, segmenting the heart and preventing fibrillation would not be possible).
Minimally invasive surgical techniques are known for performing medical procedures within all parts of the cardiovascular system. Exemplary known procedures include the steps of passing a small diameter, highly-flexible catheter through one or more blood vessels and into the heart. When positioned as desired, additional features of the catheter are used, in conjunction with associated equipment, to perform all or a portion of a medical treatment, such as vessel occlusion, tissue biopsy, or tissue ablation, among others. Almost always, these procedures are performed while the heart is beating and blood is flowing. Even though visualization and positioning aids are adequate for general placement of the device, maintaining the device in a selected position and orientation can be difficult as the tissue moves and blood flows, especially during a procedure that must be done quickly. As diagnostic and visualization equipment and techniques continue to evolve, it has become possible to identify tissue areas to be treated with greater precision while quickly situating the device and effectuating treatment.
In addition to the challenges presented by moving tissue and flowing blood, the actual topography of the tissue being treated presents challenges. For example, the interior chambers of the heart have surfaces that are irregular, uneven, and fibrous, as are the openings to the blood vessels. Thus, for procedures that call for uniform tissue contact or tissue contact along an extended line, the structure and techniques for use of known devices can be deficient in some regards. For example, catheter-based devices are known for placement in the left atrium for ablating tissue within the atrium for the purpose of electrically isolating one or more pulmonary veins from the atrium in an attempt to increase the success rate of atrial fibrillation ablation.
Depending on the requirements for a particular procedure, the target tissue that is to be ablated may be characterized as being a single spot, a series of spots or a linear ablation (i.e. a straight line or curvilinear ablation). Due to the nature and the anatomical constraints that are imposed on the procedure by the vasculature, each procedure will present unique issues for consideration. The destruction of tissue by cryoablation requires that the targeted tissue be cooled below a certain temperature. In addition, recent studies have suggested that the cooling rate and subsequent warming rate can affect the percentage of tissue cells destroyed in a cryoablation procedure.
Thus, a need for a cryogenic system is desired that will address the ablation of arrhythmias or tachycardia in atrial or ventricle heart muscles, and more particularly, to an epicardial approach which either addresses the heart directly through an open chest or employs a transcutaneous subxiphoid pericardial approach for the mapping and ablation of tachycardia using laparoscopy or thoracoscopy techniques via an epicardial or intrapericardial approach. There is also a need for a cryogenic system to address such cardiac problems by utilizing an endocardial approach with cryocatheters.
In practice, the standard ablation platform in the treatment of myocardial tissue has been radiofrequency (RF) energy. Radiofrequency energy, however, is not amenable to safely producing circumferential lesions without the potential for serious complications. In particular, while ablating the myocardial cells, heating energy also alters the extracellular matrix proteins, causing the matrix to collapse. This may be the center of pulmonary vein stenosis. Moreover, RF energy is known to damage the lining of the heart, which may account for thromboembolic complications, including stroke. The use of RF energy for ablation can lead to untoward healing responses such as collagen build up at the area of interest after treatment. In some cases, RF ablation may create lesions that cause occlusion of the coronary sinus in post procedure healing. RF also causes significant radiation exposure. A need exists for ablative devices and methods that include improved healing responses.
Although cryotherapy is finding its way into multiple areas of medicine, including cardiac surgery, there are several needs to be addressed from the actual system design, coolant delivery and return, hand-held devices, flexible probe tips and catheters, to interconnected valves, controls, and supplemental support systems. Further, in cardiac settings, the heat sink provided by the blood pool creates a tremendous challenge to current cryoablation approaches as they cannot overcome this heat extraction hurdle. New cryoablation systems, medical devices, and procedures may avoid many of these problems.